Details:RainWaterAbsorptionFactor

Rain Water Absorption Factor

The rain water absorption factor takes into account that some of the rain water hitting an inclined surface splashes off on impact and is therefore not available for capillary suction.

WUFI calculates the rain load on the component from the data in the climate file and multiplies it by the rain water absorption factor. The resulting rain quantity is offered to the component for capillary suction. (The component may imbibe the offered quantity or less, but not more).

The rain water absorption factor depends on the roughness, orientation and inclination of the surface, and on the nature of the precipitation (rain, snow...).

For horizontal surfaces, the rain water absorption factor is usually 1, since the scattered drops fall back to the surface.

For vertical surfaces, it is nearly zero for snow and hail, for other conditions it must be estimated. A value of 0.7 should be a good starting point.

Since most component surfaces - with the exception of unrendered masonry and natural stone facades - only have a moderate water absorption, they cannot imbibe all the offered water anyway. In these cases, an exact knowledge of the rain quantity is not essential (whereas the duration of the rain is still important) and estimates for the rain water absorption factor and the position-specific driving rain coefficients may be sufficient.

The rain water absorption factor is entered in the dialog Edit Surface Coefficients.